The aim of this project is to delineate biochemical mechanisms of vasoactive hormones, particularly catecholamines, dopamine, prostaglandins, and angiotensins and vasopressin in cardiovascular and renal systems. In K ion depletion, there is an inhibition of vasopressin-dependent cyclic AMP generation concentrating ability in response to vasopressin. These findings are consistent with the postulate that a part of the impaired urinary concentrating ability is at the step of cyclic AMP generation in the kidney. Maturation of cardiac response to catecholamines, and the mechanisms involved were investigated in 1 day, 1 week, 1 month and 4 month-old rabbits. The inotropic response measured by the ratio of maximum developed tension to isoproterenol and that to Ca ions was progressively increased with growth, but cyclic AMP generation in response to the isoproterenol was progressively diminished with growth, suggesting that there is maturation of inotropic response of the heart to beta adrenergic stimulation, and that mechanism is at the step after cyclic AMP generation. Dietary inorganic phosphorus (Pi) is known to affect renal handling of Pi. This laboratory observed that in addition to the effects of Pi on PTH secretion and on tubular Pi reabsorption independent of PTH secretion; dietary Pi intake affects the renal response to PTH at the step after cyclic AMP generation. Dietary Pi intake also affect renal handling of Ca ions, independent of PTH and plasma Ca ions plasma Ca. These findings suggest that there is a homeostatic mechanism on Pi an Ca ions balance in the kidney at the step after cyclic AMP generation. BIBLIOGRAPHIC REFERENCE: Beck, N., and S.K. Webster. Impaired urinary concentrating ability and cyclic AMP in K ion-depleted rat kidney. American J. of Physiology 231; 1204-1208 Oct., 1976.